Expose handlers.json from firefox profile

[llakala]

Firefox provides a way to control which file types are opened in firefox, and which file types open separate apps. This is controlled via the file path .mozilla/firefox/profile_name/handlers.json.

Home-manager provides many ways to control the firefox configuration, yet it doesn't extend to these app types. It should be fairly simple to control declaratively, since it's controlled via a simple key-value pair structure.

Here's how my personal file is structured:

{ "defaultHandlersVersion": { }, "mimeTypes": { "application/pdf": { "action":3, "extensions":["pdf"] }, "image/webp": { "action":3, "extensions":["webp"] }, "image/avif": { "action":3, "extensions":["avif"] } }, "schemes": {

    "mailto":
    {
        "stubEntry":true,
        "handlers":
        [
            null,
            {
                "name":"Gmail",
                "uriTemplate":"https://mail.google.com/mail/?extsrc=mailto&url=%s"
            }
        ]
    },
    
    "vscode": 
    {
        "action":4
    }
},
"isDownloadsImprovementsAlreadyMigrated":false

}

Most of the functions seem fairly obvious. What I call "imports" are controlled in mimeTypes, and controls what files open firefox. There are several options for what to do with this filetype, numbered from 0. I'll list what the numbers correspond to below.

• 0 corresponds to "Save File".
• 1 corresponds to “Always Ask”.
• 2 corresponds to “Use ___”. This is somewhat vague, since it applies to both using a specific binary, or using something like Gmail. It seems to just mean that it redirects into a custom handler: whether that handler is a URL or a filepath. You can control whether it links to a filepath or URL by either passing it a path, or a "uriTemplate".
• 3 corresponds to "Open in Firefox".
• 4 seems to correspond to using a default handler. I'm not totally sure on this, since I've only seen one example with VSCode. More research is required.

Then, there's what I call "exports", controlled in schemes. This manages urls of a certain scheme redirecting into an app, like Discord or VSCode. These seem to take the same actions as above. However, I haven't seem 0,or 3 used here. I'd assume that these would never occur, since it's a url, not a file. With this in mind, the only valid codes for exports would be 1, 2, or 4.

That's all the research I've done so far. Hope this helps!

[llakala]

Sorry, the file contents weren't properly formatted. This should help:

{
	"defaultHandlersVersion":
	{
	},
	"mimeTypes":
	{
    	"application/pdf":
    	{
        	"action":3,
        	"extensions":["pdf"]
    	},
    	"image/webp":
    	{
        	"action":3,
        	"extensions":["webp"]
    	},
    	"image/avif":
    	{
         	"action":3,
        	"extensions":["avif"]
    	}
	},
	"schemes":
	{
    
    	    "mailto":
    	    {
        	"stubEntry":true,
        	"handlers":
        	[
            	    null,
            	    {
                	"name":"Gmail",
                	"uriTemplate":"https://mail.google.com/mail/?extsrc=mailto&url=%s"
            	    }
        	]
    	    },
   	 
    	    "vscode":
    	    {
        	"action":4
    	    }
	},
	"isDownloadsImprovementsAlreadyMigrated":false
}

[llakala]

Found some documentation: https://mozilla.github.io/policy-templates/#handlers

[KucharczykL]

home-manager supports setting policies from the link you posted already:

programs.firefox = {
  enable = true;
  policies = {
    Handlers = {
      "schemes" = {
        "mpv" = {
          "action" = "useHelperApp";
          "handlers" = [
            {
              name = "mpv";
              path = "/run/current-system/sw/bin/mpv-handler.sh";
            }
          ];
        };
      };
    };
  };
};

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[kugland]

I did a preliminary implementation, which for now only works with the default profile. It is available on my nur-packages repo.

https://github.com/kugland/nur-packages/blob/master/modules/firefox-handlers.nix